1. Field of the Invention
The present invention relates generally to large NA optical fibers, to optical fibers suitable for use in use in data transmission system, lighting and automotive applications.
2. Technical Background
Optical data networks are increasingly attractive for use in the automotive industry because these networks offer wide bandwidth to the data links for information system, entertainment, engine management and safety functions, at a relatively low price. There are specific requirements for an optical fiber used for automotive applications. First, it is preferred that the fiber is flexible enough to allow easy handling. Second, the fiber preferably should have a high numerical aperture (NA) for easy and efficient coupling of a light source into the fiber. Third, it is preferred that the core of the fiber be large enough to minimize optical coupling loss. Currently, two types of fibers are utilized for automotive applications. The first fiber type is a Polymer Optical Fiber (POF) and the second fiber type is a Polymer Cladding Silica (PCS) fiber.
Optical networks based on POFs are good in terms of mechanical stability and costs for short point-to-point links within the passenger compartment. The main drawbacks for POFs are high attenuation (up to 0.4 dB/m between 630 nm and 685 nm) and a relatively narrow operating temperature range (about −45° C. to about +85° C.). For applications such as sensor systems for safety, engine management systems, drive-by-wire systems, and video processing systems, POF systems are limited by high attenuation and poor temperature stability.
PCS fibers provide lower attenuation and a wider operating temperature range than the POF fibers. However, PCF fibers utilize polymer (plastic) cladding in contact with and surrounding the glass core, for example fluorinated polymer. Fluorinated polymer may not have the desired thermal stability for many applications, and may delaminate from the glass core. It may also be susceptible to moisture damage. When high power sources (greater than 100 Watts) are utilized, or when the PCF fiber is operating at relatively high operating temperatures, the polymer cladding is not robust enough against heat. Under such conditions the polymer cladding carbonizes or burns, which may result in device failure, especially when the fiber is bent. In addition, the polymer cladding ages relatively quickly, losing its mechanical and optical characteristics, and becomes brittle, thus shortening device lifetime.